Over half of the world population is at risk for infection by dengue virus, a mosquito borne member of the Flavivirus family that consists of four distinct serotypes. Approximately 50 to 100 million infections occur annually resulting in an estimated 500,000 cases of life threatening dengue hemorrhagic fever or dengue shock syndrome. Due to the increased incidence and spreading geographic distribution of dengue infection, it is considered to be an emerging disease and is identified by NIAID as a category A priority pathogen. Despite the significant disease burden associated with dengue infection there is presently no approved vaccine or antiviral drug. The goal of this project is to discover and develop antiviral drugs that inhibit dengue virus infection by blocking the cell entry step in the virus life cycle. Dengue infection of host cells is mediated by the envelope protein, a class II viral fusion protein responsible for virus attachment and for triggering fusion between the virus and host cell membranes. Hawaii Biotech has expressed the envelope proteins of dengue virus in purified native form. The 3-dimensional structures of the dengue-2 envelope protein in both a pre and a post fusion state have recently been solved as a collaborative project with Stephen Harrison's laboratory at Harvard Medical School. The structures reveal two potential drug target sites on the envelope protein for inhibitors of the fusion process. One target is a hydrophobic pocket present in the native envelope of the virus particle, and the other is a channel present in the fusion intermediate form of the protein involved in the late stages of membrane fusion. These targets will be examined by molecular modeling through a process of virtual drug screening to find potential inhibitor compounds that will then be tested experimentally. The purified envelope protein undergoes the conformational rearrangements of the fusion process in vitro under appropriate conditions. This will form the basis for development of fluorescence based assay methods that can be used to identify fusion inhibitors. A cell based assay for dengue envelope mediated membrane fusion will also be developed for testing of inhibitor candidates. By evaluating two distinct molecular targets that represent different stages in the fusion process, and by exploring several different assay designs, we intend to be in a position at the conclusion of Phase I to select the best path to discovery of effective antiviral drugs for dengue and other Flaviviruses during Phase II. [unreadable] [unreadable]